1. Field of the Invention
This invention relates to the field of fluorescent lighting and more particularly to the field of circuits designed to convert electrical power derived from low frequency single or multi-phase ac service such as sixty cycle, 115 V ac to a high frequency for driving fluorescent lamps with a limited and relatively constant sinusoidal drive current; thereby making it possible to replace the costly and heavy low frequency ballast circuit typically employed in starting and driving fluorescent lamps with a light-weight, inexpensive, highly efficient, low cost circuit. The invention circuit is particularly suited for use in driving fluorescent lamps as well as HID lamps of both the high and low pressure sodium types having ratings of 50 to 500 watts.
2. Description of the Prior Art
Some presently known high frequency ballast circuits such as that discussed in "Design of Solid-state Power Supplies" by Eugene R. Hnatek, pg 470, Van Nostrand, 1981 typically use high-Q resonant circuits in shunt with the fluorescent lamp load for the purpose of developing a voltage across the lamp sufficient in amplitude to start the lamp. Circuits of this type are sensitive to the quality and tolerance of components used in their construction. The circuit in the Hnatek reference is substantially different from the present invention circuit in that the invention ballast circuit does not form a tuned tank in parallel with the load for the purpose of developing a voltage high enough to start the lamp. The invention circuit is adapted to provides a recurrent series of start pulses to ionize and start the lamp load.